Biome: A large geographical region whose climate produces a characteristic climax association of plants and animals. The term biome usually refers to terrestrial habitats (on land). In North America there are about six major biomes. Aquatic ecosystems, such as the ocean, are often subdivided into different zones, such as the intertidal, pelagic, benthic, photic and aphotic zones.

Plant Community: An assemblage or association of certain dominant indicator species occupying a given region. In California the desert biome consists of several different plant communities, such as the creosote bush scrub, shadscale scrub, sagebrush scrub, Joshua tree woodland and pinyon-juniper woodland. The local chaparral and coastal sage scrub plant communities surrounding Palomar College are condidered part of an arid desert biome. Some general biology textbooks have added a seventh biome called the "shrubland biome" to encompass these brushy habitats.

Chaparral: A plant community composed of dense, impenetrable, shrubby vegetation adapted to a Mediterranean climate with winter-wet and summer-dry seasons. The plant community is well-developed in the mountains of San Diego County. Following periodic brush fires, many of the shrub species resprout from subterranean lignotubers.

Coastal Sage Scrub: A plant community similar to the chaparral, but typically found at lower elevations (generally below 2,000 feet). Like the chaparral, many of the shrub species resprout from subterranean lignotubers. It is dominated by aromatic coastal sagebrush (Artemisia californica) and is common in the hills bordering Palomar College. Unfortunately, this plant community is prime land for developers and is rapidly being replaced by housing developments in San Diego County. It is now (2001) considered to be an endangered (threatened) plant community in southern California.

Ecosystem: All of the organisms in a natural community or biome plus all of the associated environmental factors with which they interact. The term ecosystem could actually be applied to any of the terrestrial biomes or plant communities. For example, the tundra biome could also be referred to as tundra ecosystem; the chaparral plant community could also be referred to as the chaparral ecosystem. The term ecosystem is well-suited for aquatic communities such as ponds, lakes, streams and even the ocean. In fact, oceanography is the study of the ocean ecosystem. Including ocean, topsoil and atmosphere, the earth is a large, complex ecosystem called the biosphere; however, in terms of the vast universe it is but a mere dot. A self-contained spaceship in which gasses and waste are recycled may also be thought of as an ecosystem.

Biosphere: (Earth Ecosystem): The zone of atmosphere, land and water at the surface of the earth occupied by living things. In grave danger by the effects of humans, including overpopulation, pollution and exploitation.

Environment: The sum total of physical and biotic factors that surround an organism or population of organisms.

Ecology: The study of the interrelationships between plants and animals and their environment. The term environment includes the sum total of physical and biotic conditions and influences that surround an organism or population of organisms.

Timberline in the Rocky Mountains of Colorado, showing the striking transition (ecotone) between the alpine tundra and coniferous forest biomes. Engelmann spruce at timberline become dwarfed and windswept by the ice-laden winds. The zone of timberline trees is called "krummholz," a German word meaning "crooked wood." Trees cannot survive in the frozen soil (permafrost) of the tundra. Instead this region is dominated by thick-rooted perennials and prostrate, deciduous shrubs.

The coniferous forest biome includes many different forest communities. Left: The red fir forest in the Sierra Nevada of California is dominated by the red fir (Abies magnifica var. magnifica). Right: The western slopes of the Sierra Nevada also include forests of white fir (Abies concolor) and giant sequoia (Sequoiadendron giganteum).

3. Prairie Biome

Vast herds of bison once grazed the North American prairie, from the Rocky Mountains to the Mississippi River. By the end of the 1800s, these magnificent animals were pushed to the brink of extinction by buffalo hunters. Today they survive in preserves such as the National Bison Range in Montana. During the glacial periods, rich topsoils from northern latitudes were deposited here. Perennial grasses are well-adapted to this arid region, with hot, dry summers, hard, sun-baked soils and periodic grassland fires.

4. Deciduous Forest Biome

Sassafras (Sassafras albidum) is a beautiful tree native to the deciduous forest biome of the eastern United States. It is readily identified by its large three-lobed leaves. Sassafras oil is obtained from the roots and is used in carbonated beverages, teas, medicines and perfumes.

5. Desert Biome

The North American desert biome includes several different vegetation types or plant communities. Left: A saguaro woodland (Carnegiea gigantea) in the Sonoran Desert of southern Arizona. Right: A Joshua tree woodland (Yucca brevifolia) in the Mojave Desert of California. These plant communities are dominated by drought resistant trees and shrubs and numerous species of cacti with spine-covered succulent stems containing water storage tissue.

Shadscale scrub, a California plant community dominated by low-growing species of saltbush, including Atriplex confertifolia and A. hymenelytra. This vegetation type is sometimes called a C-4 community because some of the dominant members exhibit C-4 photosynthesis. Plants with C-4 photosynthesis are photosynthetically efficient even during the hot summer months when many C-3 species become dormant.

The tropical rain forest contains tall trees draped with epiphytes and vines. In the left photo a large sea heart vine (Entada gigas) connects the limbs of two adjacent trees. In Costa Rica, this vine is known as escalera de mono or "monkey ladder," and actual forms arboreal thoroughfares for monkeys high in the rain forest canopy. Along the edge of the forest where there is abundant sunlight, the sea heart vines completely cover their support trees (center). The right photo shows how the rain forest is rapidly being cut down to provide more agricultural land. Unfortunately, the soil is poor and only supports crops for a few years.

The aerial roots of strangler figs are a conspicuous element of tropical rain forests. Left: Ficus citrifolia in the U.S. Virgin Islands (Island of St. John). Right: Ficus cotinifolia in the Yucatan Peninsula of Mexico. In both photographs, the host tree has been shaded out and killed by the strangler fig.

7. Urban Sprawl

Aerial view of San Diego on the approach to the International Airport (Lindbergh Field). This dense mass of congested buildings and concrete is a good example of an urbanized human community.

During the last three decades of the 20th century, numerous grassy hillsides in coastal San Diego County were converted into high density housing tracts. Some of these grassland habitats on thick clay soils contained an abundance of rare and endangered wildflowers (red arrow), such as the striking chocolate lily (Fritillaria biflora).